Researchers at Japan’s JAIST institute have developed an additive for graphite anodes in lithium-ion batteries. Cells with the new additive retained 95.6% of their initial capacity after 1,000 charge cycles, Interesting Engineering reports.
Battery degradation over time is a well-known problem, even if it’s not severe enough in today’s EVs to bother a first owner. JAIST scientists added a compound called pentafluorophenyl thiophene imine (FPTI) to the graphite anode’s chemical makeup. During the first few charge cycles, it forms a protective film on the anode’s surface that slows down further degradation.
That protective layer lets lithium ions move between the electrolyte and the anode without triggering unwanted chemical reactions. When the layer is unstable, active lithium consumption and electrical resistance both rise, and the cell loses capacity faster. In the experiment, researchers added FPTI to the electrolyte at concentrations of 2 to 4 mg per milliliter. The additive produced a more stable, yet still conductive, coating on the graphite anode.
The additive’s complex molecular structure affects the battery differently depending on the component. Sulfur- and imine-based compounds join the protective layer, while fluorine enriches lithium compounds on the surface. Together, they cut down on unwanted side reactions and smooth the movement of lithium ions across the electrode-electrolyte interface. Cells with a 2 mg/mL concentration retained 89.4% of their initial capacity after 1,000 cycles. Bumping the concentration to 4 mg pushed that figure to 95.6%. A control cell with no additive held onto just 62.7% of its capacity over the same period, with a sharp decline setting in after only 350 cycles.
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Adding FPTI directly to a finished cell’s electrolyte, however, raised cathode resistance and hurt performance in NMC (nickel-manganese-cobalt) cells. That means the additive only works when applied during anode preparation, before the cell is assembled with a standard electrolyte.
The additive also boosted energy density. A cell with 4 mg/mL of FPTI saw its charge storage density climb from 130 to 233 Wh/kg, while a 2 mg/mL concentration pushed it to 192 Wh/kg. Bringing the additive to mass production will require large-scale testing, but the researchers say the experiment shows conventional lithium-ion batteries still have plenty of room left for improvement.
